1. Field of Invention
The present invention relates to RF systems. More specifically, the present invention relates to phased array antenna systems used for RF systems and other applications.
2. Description of the Related Art
For many applications, it is necessary or desirable to be able to automatically track a received signal. In a radar or communication application, for example, it might be useful to be able to track a source of a received signal. A satellite or another RF signal, for example, might be tracked and a return signal automatically transmitted back to the satellite or RF signal source in response thereto. Hence, an automatic tracking system might allow for more effective and efficient direction of a return beam to complete an RF signal source or communication link.
Conventionally, beam tracking has involved physically pointing an antenna in the direction of the received beam and processing the received signal with a tracking algorithm to steer the antenna in the direction of the received signal. This approach can be problematic inasmuch as it requires the steering of a physical antenna and is therefore relatively computationally intensive, slow and costly.
Thus, while phased array antennas have been used for some time, automatic beam steering in response to an RF signal with a phased array antenna has been somewhat problematic to date.
Hence, a need remains in the art for an improved system and method for automatically tracking a beam and steering a transmit beam in response thereto.
The need in the art is addressed by the system and method of the present invention. The inventive system includes a first mechanism for receiving a first signal having a first wavefront from a first direction. A second arrangement provides a second signal having a second wavefront. The second signal is a phase conjugate of the first signal. A third mechanism is included for transmitting the second signal. The second signal is transmitted in a reverse direction relative to the direction of the first signal.
In the illustrative embodiment, the first mechanism is a phased array antenna comprising a plurality of radiating elements and the first signal is a radio frequency signal. The wavefront that is received, phase conjugated and transmitted is a sampled wavefront of the wavefront being received. The second arrangement includes a plurality of phase conjugators each of which are coupled to an associated radiating element to receive an input signal therefrom. The phase conjugator output has a signal which is the negative of the first signal""s phase and this output is then transmitted. In an illustrative embodiment, the second arrangement also includes a plurality of phase conjugators each of which are coupled to an associated radiating element to receive an input signal therefrom. Each of the phase conjugators includes a mixer, as the phase conjugator, said mixer having the input signal as a first input thereto. The input signal has a first frequency and a first phase. A second signal having a frequency equal to twice the first frequency is input to each mixer such that the output of the mixer includes a component representative of the negative of the first phase. The output of each mixer is filtered to extract the component representative of the negative of the first phase and transmitted.
The inventive method, then, involves an adaption of a radar (or other suitable system) to utilize phase conjugation, where phase conjugation means reversing the phase factor of the incident wavefront. A phase conjugated RF wavefront, for example, propagates backward in space and time with the same wavefront as the original incoming wave. In the illustrative embodiment, the invention uses a received RF signal from an RF source as a sampled reference signal to be phase conjugated by the radar phased array antenna. Phase conjugation of an Electromagnetic (EM) wavefront using an antenna array can be described as the process of automatically configuring the phased-array antenna system to direct its outgoing signals to retrace *an incoming signal""s path exactly back to its source. This automatic signal redirection capability is provided by using a phase conjugation technique in each transmit/receive. (T/R) module of a phased array radar. The illustrative technique is to use a mixer in each T/R module to generate the phase conjugated signal by mixing the sampled received signal wavefront with a signal that is twice the frequency of the received signal. This above operation can occur for a plurality of received signal wavefronts, each from a different direction, as long as each RF signal is within the field of regard of the antenna. The field of regard can be defined in general as the antenna beamwidth of an individual antenna radiator.